On Fri, Jan 17, 2014 at 9:14 AM, Andres Freund <andres@2ndquadrant.com> wrote:
> The scheme that'd allow us is the following:
> When postgres reads a data page, it will continue to first look up the
> page in its shared buffers, if it's not there, it will perform a page
> cache backed read, but instruct that read to immediately remove from the
> page cache afterwards (new API or, posix_fadvise() or whatever). As long
> as it's in shared_buffers, postgres will not need to issue new reads, so
> there's no no benefit keeping it in the page cache.
> If the page is dirtied, it will be written out normally telling the
> kernel to forget about the caching the page (using 3) or possibly direct
> io).
> When a page in postgres's buffers (which wouldn't be set to very large
> values) isn't needed anymore and *not* dirty, it will seed the kernel
> page cache with the current data.
This seems like mostly an exact reimplementation of DIRECT_IO
semantics using posix_fadvise.
--
greg